And employers complain that teenagers rely on a narrow vocabulary and do not understand the importance of formal speech, said Prof McEnery, a linguistics specialist from Lancaster University.

Prof McEnery analysed 10 million words of transcribed speech, 100,000 words gathered from teenagers' blogs and research among 200 youngsters for his study, conducted for Tesco.

He said: "While not expecting to find it in advance of doing the research, I was struck by how accurate the 'Vicky Pollard' stereotype is.

"It is clearly a well observed piece of comedy. 'Her' speech is confrontational in exactly the way that the list predicts - even down to 'yeah', 'but' and 'no' being typical teenager words.

"While not wanting to criticise teenage speech unduly, there is a serious point in the study that educators may reflect upon.

"If, as appears to be the case, teenage speech is markedly informal, perhaps it is the case that there is a strong case to be made for teenagers to be given more explicit instruction on when it is appropriate - and when it is not appropriate - to use informal modes of speech.

"Such a proposal is uncontroversial in writing - children are typically taught how to produce formal writing styles, for example letters, at school.

"Why should they not also be taught how to produce speech in formal situations?"

A limited vocabulary will restrict children's creativity and curtail their powers of expression, he said.

Prof McEnery went on: "Employers are already complaining that first jobbers are lacking basic verbal communication and it seems things could be set to get worse.

"This is becoming a key issue for linguists, as there is a debate about whether speech is deteriorating not simply in teenagers, but in infants.

"This has very far reaching effects indeed and it could well be that as the 'TV generations' grow up a serious decay of oral language skills, including vocabulary, will become a key issue in education."

The report was published as Tesco launched a £750,000 initiative aimed at improving pupils' communication skills by giving free internet phones to schools.